1. Field of the Invention
The present invention relates to a fuel cell system including a fuel cell and, more particularly, relates to a fuel cell system in which a water component contained in the gas exhausted from a fuel cell is utilized for humidifying the process air before air enters the fuel cell.
2. Description of the Related Art
Japanese Unexamined Patent Application (Kokai) No. 7-14599 (JP-A-""599) discloses a fuel cell system of which the basic construction and arrangement are shown in FIG. 2. In FIG. 2, process air is supplied via an air-supply line 3 to an air compressor 6 driven by a drive motor 30, and is compressed to a predetermined pressure. The compressed process air is supplied to a fuel cell 12. The fuel cell 12 uses the oxygen component in the process air and discharges the process air as an exhaust gas into a discharge line 5 in which an energy-recovery unit or an expander 16 is arranged to be connected to the air compressor 6 via a common shaft 20. The exhaust gas is expanded by the expander 16 and is discharged into the atmosphere.
Produced water contained in the exhaust gas exhausted from the fuel cell 12 is separated from the gas component by liquid-gas separators 18 and 24 respectively arranged in the discharge line 5. The produced water is subsequently collected into an open water tank 7 from which the water is pumped by a hydraulic pump 8 and is supplied to an injection nozzle 10 by which the water is injected into the process air to humidify the process air supplied into the fuel cell 12.
It will be understood from the foregoing description that, in the fuel cell system of JP-A-""599, the water component contained in the exhaust gas is separated by the liquid-gas separators 18, 24 to be collected into the water tank 7 from which the water is recycled to the air-supply line 3 to humidify the process air. Nevertheless, JP-A-""599 fails to disclose how to cool and lubricate the air compressor 6. Further, since the fuel cell system of JP-A-""599 must use the water pump 8 to deliver the water from the water tank 7 to the injection nozzle 10, it is difficult to employ this fuel cell system as a fuel cell system mounted on a vehicle from the viewpoint of easily mounting it in a mounting space in the vehicle. In addition, the employment of the water pump 8 will surely lead to an increase in the manufacturing cost of a fuel cell system.
An object of the present invention is to eliminate unfavorable problems encountered by the convention fuel cell system as disclosed in JP-A-""599.
Another object of the present invention is to provide a fuel cell system incorporating therein a fuel cell and able to humidify the process air supplied to the fuel cell and to cool and lubricate a gas compressor without a water pump to deliver the water.
In accordance with the present invention, there is provided a fuel cell system which comprises:
a fuel cell having at least an air inlet and an exhaust gas line;
a gas compressor connected to an air-supply line through which process air is supplied from the gas compressor into the fuel cell, the gas compressor having at least a compression chamber, a suction port, a delivery port and a water-supply port;
a recovery unit arranged in the exhaust gas line through which an exhaust gas containing therein produced water is discharged from the fuel cell;
a liquid-gas separating unit arranged in the exhaust gas line between the fuel cell and the recovery unit for separating the produced water from the exhaust gas, the liquid-gas separating unit having a water storing vessel for storing the produced water separated from the exhaust gas;
a water-supply line connecting between the water storing vessel of the liquid-gas separating unit and the water-supply port of the gas compressor; and
a pressure-supply means for applying the pressure of the exhaust gas to the produced water stored in the water storing vessel to thereby deliver the produced water from the liquid-gas separating unit into the water-supply line.
Preferably, the gas compressor is provided with a suction port for the process air and at least one compression chamber which is supplied with a water via the water-supply port when the compression chamber is completely closed to confine therein the process air sucked from the suction port.
Preferably, a flow control valve is arranged in the water-supply line to regulate the flow rate of the water flowing through the water-supply line in response to detection of a predetermined signal indicating an operating condition of the gas compressor.
Further preferably, the predetermined signal indicating the operating condition of the gas compressor comprises a humidity signal indicating the humidity of the process air delivered from the gas compressor toward the fuel cell.
Preferably, the predetermined signal indicating the operating condition of the gas compressor comprises a flow signal indicating the flow rate of the process air delivered from the gas compressor toward the fuel cell.
The fuel cell system is preferably provided with a subsidiary water vessel fluidly connected to the liquid-gas separating unit for receiving excess water overflowing the liquid-gas separating vessel when the water stored in the liquid-gas separating unit exceeds a predetermined limiting level.
Since the pressure of the exhaust gas exhausted from the fuel cell is constantly applied to the surface of the water separated from the exhaust gas and stored by the liquid-gas separating unit, the water can be supplied into the water-supply port of the gas compressor via the water-supply line without the assistance of a liquid pump. Thus, the supplied water is able to perform cooling and lubricating of the gas compressor as well humidifying the process gas supplied to the fuel cell. At this stage, since the water-supply port of the gas compressor is arranged so that the water supplied into the compression chamber when the compression chamber is completely closed to confine therein the process air sucked from the suction port, there occurs neither leaking of the water from the gas compressor toward the exterior of the gas compressor, without it being delivered together with the compressed process air, nor a reverse-flow of the water from the compression chamber toward the water-supply port and the suction port. Namely, the water can be surely confined in the compression chamber together with the process air to humidify the air and it is subsequently discharged from the compression chamber while absorbing the compression heat. Thus, cooling of the gas compressor as well as lubrication of movable elements of the compressor such as a rotor, vanes, a movable scroll element and bearings can be achieved.